In conventional, there has been a vane type variable valve timing control apparatus for variably controlling an opening and closing time of an intake or exhaust valve in an engine by variably controlling a rotational phase of a cam shaft driven by a crank shaft of the engine via a chain sprocket or the like, and an opening and closing timing control method using the same.
The vane type variable valve timing control apparatus is provided with a vane rotor integrally rotating with a cam shaft in an inner portion of a timing pulley, and an advance hydraulic chamber and a retard hydraulic chamber rotating the vane rotor to an advance side or a retard side. The vane rotor rotates to the advance side or the retard side by supplying and discharging the hydraulic pressure to the advance hydraulic chamber and the retard hydraulic chamber in correspondence to the engine operation state, and changes a phase of the opening and closing time of the intake or exhaust valve on the basis of a change of the rotational phase of the chain sprocket and the cam shaft generated thereby.
In this case, positive and negative rotational variable torques caused by a spring force of a valve spring or the like are applied to the cam shaft controlling the opening and closing time of the intake or exhaust valve. Accordingly, when the rotational variable torque is applied in the act of rotationally driving the vane rotor to the retard side or the advance side, the rotational variable torque becomes larger than the vane rotor driving hydraulic pressure, so that a phenomenon that the vane rotor is pressed back is generated. Therefore, there is a problem that a response of the opening and closing time control of the intake or exhaust valve is lowered.
Further, the oil pump used as a hydraulic pressure source is rotationally driven in synchronous with a crank shaft of the engine, and a discharge amount thereof is approximately in proportion to an engine rotational speed. Accordingly, there is generated a problem that it is impossible to secure a sufficient power for driving the vane rotor or a sufficient response in the case that the engine rotational speed is low, in comparison with the case that the engine rotational speed is high.
Accordingly, as described in JP-A-2002-235513, there are provided a switch means for selecting advance and retard directions, and a check valve operating on the basis of the positive and negative change of the variable torque. Therefore, it is possible to intend to improve the response by utilizing a hydraulic pressure generated in the variable torque in the advance direction at a time of the advance and a hydraulic pressure generated in the variable torque in the retard direction at a time of the retard, in addition to driving of the vane rotor on the basis of the normal supply and discharge of the hydraulic pressure with respect to the advance hydraulic chamber and the retard hydraulic chamber.
In JP-A-2001-317382, there is described a structure which is provided with an energizing means, and a control means for controlling a valve timing in addition to an energizing force of the energizing means.
In JP-A-2002-168103, there is described a structure which is provided with a hydraulic pressure supply and discharge means for relatively supplying and discharging a hydraulic pressure generated in a hydraulic pressure source with respect to an advance hydraulic chamber and a retard hydraulic chamber, by selectively communicating from the retard hydraulic chamber to the advance hydraulic chamber.
The technique described in the JP-A-2002-235513 showing the prior art mentioned above is of a type utilizing the hydraulic pressure generated in the variable torque in the advance direction at a time of the advance and the variable torque in the advance direction at a time of the retard time, by the switch means for selecting the advance and retard directions, and the check valve operating on the basis of the positive and negative change of the variable torque. However, since the check valve operating on the basis of the positive and negative change of the variable torque is operated only after the change of positive angle of the variable torque is generated, a time lag is necessarily generated in opening and closing the check valve. Accordingly, there is a problem that the variable torque in an opposite direction to a direction to be rotated is applied only for a short time.